1. Field of the Invention
The present invention relates to an optical fiber resin coating apparatus, more particularly, an optical fiber resin coating apparatus for uniformly coating a resin on an optical fiber at a high speed.
2. Description of the Related Art
An optical fiber consisting of a core and a cladding provided at an outer circumferential of the core is produced by heating a preform of the optical fiber at a furnace and drawing it out from the furnace. Thereafter, the optical fiber is coated by a resin to produce a resin coated optical fiber.
Japanese Unexamined Patent Publication (Kokai) 6-279047 discloses a technology for coating a resin on an optical fiber. FIG. 1 is a sectional view of an optical fiber resin coating apparatus of Japanese Unexamined Patent Publication (Kokai) 6-279047.
For coating resin on an optical fiber, in addition to the optical fiber resin coating apparatus shown in FIG. 1, as disclosed in Japanese Unexamined Patent Publication (Kokai) 6-279047, it is necessary to provide a resin supply means for supplying a resin to the optical fiber resin coating apparatus, a moving means for introducing an optical fiber into the optical fiber resin coating apparatus and drawing out a resin coated optical fiber from the optical fiber resin coating apparatus, a cooling means for cooling the drew out hot resin coated optical fiber, an outer diameter measurement means for measuring an outer diameter of the resin coated optical fiber, a control means for reading the measured outer diameter and controlling a drawing-out speed of the moving means, and resin supply parameters at the resin supply means, and a winding means for winding the cooled resin coated optical fiber. Below, the optical fiber resin coating apparatus in FIG. 1 will be described in detail.
The optical fiber resin coating apparatus is formed as an assembly 3 of a combination of a nipple 1 and a resin coating die 2.
A resin flow path 4 is defined at the gap (a boundary portion or an interface) of the nipple 1 and the resin coating die 2. A nipple hole 5 of the nipple 1 and a die hole 6 of the resin coating die 2 are aligned in the assembly 3 at a same center line. The nipple hole 5 is constituted by a tapered-hole portion 5a and a land portion 5b. A resin supply chamber 7 is provided in the coating die 2 in a concentricity with the die hole 6. A resin supply inlet 8 is also provided in the coating die 2 to supply a resin 9 to the resin supply chamber 7. An optical fiber 10 is introduced into the nipple hole 5 and the die hole 6 to be coated with the resin 9. The resin 9 is supplied to the die hole 6 at a predetermined pressure from the resin supply chamber 7 through the resin flow path 5, to produce a resultant resin coated optical fiber 11.
A meniscus-shaped portion 12, which is a boundary plane of the resin 9 and the optical fiber 10, is formed at an outlet portion of the nipple hole 5, and a circular flow 13 of the resin 9 is caused in a cavity formed inside of tapered-hole portion 6a of the die hole 6 in the resin coating die 2.
The optical fiber resin coating apparatus disclosed in Japanese Unexamined Patent Publication (Kokai) 6-279047 suffers from the disadvantages of a partial lack (partial failure) of the coating of the resin on the optical fiber 10 in certain portions and/or unevenness of the diameter of the resin coated optical fiber 11 when the resin coated optical fiber 11 is drawn out from the optical fiber resin coating apparatus a high speed. Accordingly, the optical fiber resin coating apparatus of Japanese Unexamined Patent Publication (Kokai) 6-279047 suffers from the disadvantage of a limitation of the speed up of the drawing-out speed. Consequently, the optical fiber resin coating apparatus of Japanese Unexamined Patent Publication (Kokai) 6-279047 can not achieve a high productivity of the resin coating.
Japanese Examined Patent Publication (Kokoku) 7-91092 discloses a technology for preventing the partial lack (failure) of the coating and/or unevenness of the diameter of the resin coated optical fiber by suitably defining (designing) the size of the resin flow path 4 and the angle of the tapered-hole portion 6a in the resin coating die 2.
The technology of Japanese Examined Patent Publication (Kokoku) 7-91092 can provide a good result below the drawing speed of the resin coated optical fiber is 1000 m/min, but still suffers from the disadvantages of the partial lack (failure) of the coating and/or unevenness of the diameter of the resin coated optical fiber at higher speed drawing.
According to an analysis of such disadvantages by inventors of the present invention, it was found that the reasons of the partial lack of the resin coating and/or the unevenness of the diameter of the resin coated optical fiber during high speed drawing had probably been due to disruptions in the circular flow 13 in the cavity of the tapered-hole portion 6a of the resin coating die 2 during high speed drawing. Namely, the high speed drawing of the resin coated optical fiber 11 disrupted the smooth circular flow in the cavity of tapered-hole portion 6a and caused vibration of the moving optical fiber 10 and destabilized the meniscus-shaped portion 12 formed at the outlet portion of the nipple hole 5.
The countermeasures of the technology disclosed in Japanese Examined Patent Publication (Kokoku) 7-91092 run up against the disadvantages of the limit on speed of Japanese Unexamined Patent Publication (Kokai) 6-279047.